title: Solution interactions between the uranyl cation [UO2(2+)] and histidine, N-acetyl-histidine, tyrosine, and N-acetyl-tyrosine.
abstract: Complexes of the uranyl cation [UO(2)(2+)] with histidine (His), N-acetyl-histidine (NAH), tyrosine (Tyr), and N-acetyl-tyrosine (NAT) were studied by UV-visible and NMR spectroscopy, and by potentiometric titration. Protonation constants for each ligand are reported, as are cumulative formation constants for uranyl-amino acid complexes. Coupling constant data (J(CH)) for uranyl-histidine complexes indicate that inner-sphere solution interactions between histidine and uranyl cation are solely at the carboxylate site. At 25 degrees C the major uranyl-histidine complex has a cumulative formation constant of logbeta(110)=8.53, and a proposed formula of [UO(2)HisH(2)(OH)(2)](+); the stepwise formation constant, logK(UL), is estimated to be 5.6 ( approximately 8.53-(-6.1)-(-6.1)-15.15). Outer-sphere interactions, H-bonding or electrostatic interactions, are proposed as contributing a significant portion of the stability to the ternary uranyl-hydroxo-amino acid complexes. The temperature dependent protonation constants of histidine and formation constants between uranyl cation and histidine are reported from 10 to 35 degrees C; at 25 degrees C, DeltaG=-43.3 kJ/mol.
authors.affiliation: Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110, United States.
authors.forename: Wei
authors.initials: W
authors.lastname: Xie
authors.forename: Ahmed
authors.initials: A
authors.lastname: Badawi
authors.forename: Huan
authors.initials: H
authors.lastname: Huang
authors.forename: J David
authors.initials: JD
authors.lastname: Van Horn
mesh_terms: D002413:Cations, Divalent; D006639:Histidine / Q000031:analogs & derivatives* / Q000737:chemistry; D006868:Hydrolysis; D007093:Imidazoles / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000737:chemistry; D017974:Uranium Compounds / Q000737:chemistry*
chemical_list: D002413:Cations, Divalent; D007093:Imidazoles; D012996:Solutions; D017974:Uranium Compounds; D014443:Tyrosine; D006639:Histidine; C029899:imidazole; C025787:N-acetyltyrosine; C023495:N-acetylhistidine; C012597:uranium dioxide